1. Field of the Invention
The present invention relates to fine barium titanate based powder having a high dielectric constant and a low temperature coefficient of capacitance. The barium titanate based powder in accordance with the present invention has high sintering density, low dielectric loss and high insulation resistance. The present invention also relates to a dielectric material including the fine barium titanate based powder and a ceramic electronic part including the dielectric material.
2. Description of Related Art
Since barium titanate (BaTiO3) has a high dielectric constant and excellent polarization hysteresis and piezoelectric effect, and may impart semiconductive property with ease upon the addition of a dopant, it has been widely used as a material for ceramic electronic parts, such as ceramic capacitors, amplifiers, memory devices, modulators, electroacoustic transducers, actuators, other piezoelectrics, positive thermistors, semiconductors, etc. Particularly, tetragonal barium titanate is a ferroelectric, and thus has a very high dielectric constant and polarization hysteresis. Therefore, tetragonal barium titanate is widely used as a dielectric material in multi-layer ceramic capacitors (MLCCs).
Recently, as electronic instruments have been miniaturized rapidly, it has been required for ceramic electronic parts to have a compact size and high capacity. Particularly, in the case of a MLCC, it has been required for a dielectric layer to have a small thickness and to be stacked in a higher number. Because the number of barium titanate particles that can be contained in one dielectric layer is limited, barium titanate should be provided as finer particles as the dielectric layer has a smaller thickness. Therefore, many attempts have been made to maintain a high dielectric constant despite the provision as fine particles, to minimize a temperature coefficient of capacitance, and to improve a sintering density, dielectric loss and insulation resistance, so that barium titanate may be applied to a high-capacity MLCC.
For example, Korean Laid-Open Patent No. 2002-0048101 discloses a method for preparing barium titanate powder for X7R MLCCs, including: mixing and drying starting materials formed of barium carbonate (BaCO3) and titanium dioxide (TiO2) and calcinating the resultant mixture; pulverizing the resultant powder crudely, adding thereto additives containing an acceptor, a doner, a particle growth inhibitor and a sintering aid in an amount of 1.6-4.0 g per 100 g of the powder, and finely pulverizing the resultant mixture; drying the mixed powder containing the additives and further calcinating the powder; and further pulverizing the resultant powder crudely, followed by additional fine pulverization. However, the resultant particles are too crude to be applied to a high-capacity MLCC and have a large temperature coefficient of capacitance.
Japanese Laid-Open Patent No. 2008-156202 discloses a dielectric ceramic including grains based on barium titanate and grain boundaries formed among the grains, the dielectric ceramic being characterized in that it includes, per mole of barium forming the barium titanate, 0.01-0.06 moles of magnesium as expressed by MgO, 0.0015-0.03 moles of yttrium as expressed by Y2O3 and 0.0002-0.03 moles of manganese as expressed by MnO, further includes 4.2-33.3 parts by weight of niobium as expressed by Nb2O5 per 100 parts by weight of barium titanate, and has an average particle diameter of the grains of 0.05-0.2 μm. However, the dielectric ceramic has a very low dielectric constant so that it may not be applied to a high-capacity MLCC.
In general, barium titanate having a smaller particle diameter has a lower ferroelectric tetragonal phase content and a higher paraelectric cubic phase content, resulting in a drop in dielectric constant and a decrease in capacitance. In conclusion, according to the related art, it is not possible to provide barium titanate based powder in the form of fine particles having a high dielectric constant and a low temperature coefficient of capacitance, and satisfying some electrical properties, such as sintering density, dielectric loss and insulation resistance, applicable to a ceramic capacitor.